production
Seaweed Aquaculture Provides Diversified
Products, Key Ecosystem Functions
Part I. Lesser-Known Species Group Tops Mariculture Output
beaches in tropical regions are, in fact,
made of fine debris of dead, calcified
green seaweeds.
Image Issues
When harvesting red seaweed, specialized boats go under the nori nets. The Porphyra
yezoensis is processed into wrappers for sushi rolls.
Dr. Thierry Chopin
University of New Brunswick
Canadian Integrated Multi-Trophic
Aquaculture Network
P. O. Box 5050
Saint John, New Brunswick
E2L 4L5 Canada
[email protected]
Summary:
Seaweeds play key roles in Earth
processes and are the world’s
largest mariculture crop. They are
primary producers and links in
the food webs of coastal and estuarine ecosystems, and are used
in many applications that affect
our everyday lives. About 220
species of seaweeds are cultivated
worldwide, primarily in Asia. It
has been estimated that the productivity of seaweed communities
is equal to or greater than that
of the most productive terrestrial
plant communities.
Seaweeds belong to one of the less
known and appreciated groups of marine
organisms on this planet, while playing
42
May/June 2012
key roles in Earth processes and being the
largest mariculture crop. They are used in
many diverse applications, making them
part of our everyday lives.
You may start your day with seaweeds
in your orange juice, where a microscopic
mesh of carrageenans extracted from red
seaweeds keeps the pulp in suspension.
You may also end your day with seaweeds, as your toothpaste would be a liquid without alginates extracted from
brown seaweed.
Roles In Nature
Did you know that every second molecule of oxygen we inhale was produced by
micro- or macroscopic algae, and every
second molecule of carbon dioxide we
exhale will be reused by these algae? Algae
initiated an irreversible global change that
led to the current oxygen-rich atmosphere,
and by transferring atmospheric carbon
dioxide into organic biomass and sedimentary deposits, they now act as a carbon sink
that slows down global warming.
Seaweeds are key primary producers
and links in the food webs of coastal and
estuarine ecosystems, where they participate naturally in nutrient recycling and
waste management. Coral reefs would
not have been formed without the help of
seaweeds. Many of the white “sandy”
global aquaculture advocate
Unfortunately, seaweeds are often
seen as rather unpleasant organisms.
They are very slimy and slippery, and can
make swimming or walking along the
shore an unpleasant experience.
Seaweeds have also recently attracted
media coverage in reports of outbreaks of
“green tides” and fouling species, which
are considered nuisances. It is important
however, to emphasize that green tides
are not the cause, but the consequence of
coastal nutrification, which needs to be
addressed by long-term integrated coastal
zone management.
Seaweeds Are…
A simple definition of seaweed is not
that simple, because this heterogeneous
group is only a fraction of an even less
natural assemblage, the “algae.” Algae are
a diverse group of organisms that share
only a few characteristics. They photosynthesize and provide oxygen. They do
not make flowers, and their anatomy is
relatively simple, with no roots, stems,
leaves or vascular tissues, and simple
reproductive structures.
With progress in molecular techniques, we realize this “mixed bag” contains species spread over most kingdoms
of organisms, encompassing microscopic
microalgae like the unicellular phytoplanktonic forms and macroscopic macroalgae like the giant kelps that grow
taller than trees. Algae colonize the
oceans, freshwater streams, trees (associated with fungi in lichens), stones, snow
in high-altitude glaciers, geothermal
sources and even deserts.
The largest of all algae, the giant kelp,
Macrocystis pyrifera, can grow to up to 50
m long. One of the fastest-growing organisms on Earth, the kelp can grow as much
as 61 cm daily. The smaller sugar kelp,
Saccharina latissima, can reach 11 m in
length, with a growth rate as high as 2 cm/
day. It has been estimated that the primary
Seaweeds in a tide
pool in the Bay of
Fundy, New Brunswick, Canada. The
kelps are already
farmed and others
are candidates for
future aquaculture
development.
still be considered plants, they do not
have much in common. The well-known
green seaweed sea lettuce (Ulva) is closer
at the molecular level to a spruce tree
than to the well-known red seaweed nori
(Porphyra), even if their morphology is
very similar, and they are found close to
one another on the shore.
Needless to say, the classification of
algae is still the source of constant changes
and controversies among scientists. The
fact that the 36,000 known algae represent
only about 17% of the existing algal species is a measure of our still-limited
knowledge of this group of organisms,
despite their key roles on this planet.
One of the key reasons for regularly
ignoring seaweeds, even in coastal studies,
is the very problem of their identification,
as very few people, even among scientists,
can identify them correctly. The production of seaweeds has probably been underestimated, since it may approach 10% of
that of all the phytoplankton. However,
that is taking place in 0.1% of the area
occupied by phytoplankton, and this
coastal zone area is crucial.
It is estimated that this year, aquaculture will account for over 50% of the
world’s consumption of food fish, defined
as finfish, crustaceans, mollusks and other
aquatic animals for human consumption.
About 94% of the world seaweed supply
presently comes from aquaculture, and
seaweeds were the first group of organisms
to pass the 50% farmed/wild harvest
threshold in 1971. This occurred in 1986
for freshwater fish, in 1994 for mollusks,
in 1997 for diadromous fishes and in 2010
for crustaceans. Marine fish production is
still far from achieving this threshold.
Seaweed Mariculture
There are approximately 10,500 known
species of seaweeds. Around 500 have been
used for centuries for human food and
medicine, directly or indirectly as extracted
phycocolloids such as agars, carrageenans
and alginates. However, only approximately
220 species of seaweeds are cultivated.
The largest group of organisms cultured at sea is seaweeds. Their production
represents 46% of the total world mariculture, while fish aquaculture represents
only 9%. Almost all the 15.8 mmt of cultivated seaweeds – worth U.S. $7.4 billion annually – come from China, Indonesia, the Philippines, Korea and Japan.
Unfortunately, seaweeds are systematically short changed in seafood statistics,
which tends to limit the Western world’s
knowledge of seaweeds (Figure 1).
Figure 1. World mariculture production
of major species groups, 2008.
global aquaculture advocate
May/June 2012
43